Spatial and temporal heterogeneity in the distribution of an Antarctic amphipod and relationship with the sediment

The nearshore Antarctic environment is subject to increasing anthropogenic impact, yet the ecological processes influencing some of its most dominant species remain poorly understood. We examined patterns of the distribution and abundance of the Antarctic amphipod Orchomenella franklini in relation to the local environment. Samples of benthic sediment were collected in East Antarctica across several spatial and temporal scales and were analysed for the abundance of O. franklini and various sediment properties. O. franklini was found to reach extremely high densities (<41000 m^-2), yet abundance was strongly heterogeneous on all spatial scales tested. Temporal variation in abundance was also significant and was location-specific, potentially reflecting fluctuations in food supply and variable conditions resulting from ice disturbance. Principal component analysis and generalised additive modelling revealed evidence of a relationship between the distribution of O. franklini and the sediment, which was consistent with its deposit-feeding trophic niche. Generally, the abundance of O. franklini increased with decreasing sediment grain size and increasing trace element concentration. Abundance also peaked at high (though not maximum) total organic carbon content. This is one of the first empirical demonstrations of a correlation between discrete physical sediment traits and the abundance of an infaunal benthic species in the Antarctic, with evidence consolidated from 2 geographic regions. The influence of local conditions on the abundance of O. franklini provides insight on the heterogeneity of Antarctic benthic ecosystems.